Steering device for motor vehicle

ABSTRACT

There is disclosed a steering apparatus for a vehicle in which a steering power of a steering shaft is assisted by a column-assist type electric power steering apparatus so that the steering power is transmitted to steer the wheels by means of a steering mechanism, in which a telescopic shaft with a male shaft and a female shaft fitted to each other to be mutually unrotatable and slidable is interposed between an output shaft of said column-assist type electric power steering apparatus and an input shaft of the steering mechanism.

TECHNICAL FIELD

The present invention relates to a steering apparatus for a vehicle inwhich a steering power of a steering shaft is assisted by acolumn-assist type electric power steering apparatus so that thesteering power having increased torque is transmitted through atelescopic intermediate shaft to steer the wheels by means of a steeringmechanism in its turn.

BACKGROUND ART

In Japanese Utility Model Application Laid-Open No. 1-145670, anintermediate shaft is interposed between an output shaft of acolumn-assist type electric power steering apparatus and a pinion shaftof a steering gear. This intermediate shaft is provided with a damperfor damping a reaction force from a road surface. This intermediateshaft, however, is not extended and/or contracted in the axialdirection.

FIGS. 9 to 12 show a steering apparatus for a vehicle according to aprior art. According to the prior art, an intermediate shaft which iscollapsible at a secondary collision is interposed between an outputshaft of a column-assist type electric power steering apparatus and apinion shaft of a steering gear.

That is, FIG. 9 is a schematic view of the steering apparatus for avehicle according to the prior art. In FIG. 9, a steering column 50 isrotatably supported by a steering shaft 51, and a steering wheel 52 isprovided in an upper part of the steering shaft 51.

The steering column 50 is provided with a column-assist type electricpower steering apparatus 53, and this electric power steering apparatus53 is provided with an electric motor 54 for assist, a gear unit 55serving as a reduction gear, an output shaft 56 for outputting asteering power assisted by the electric motor 54 with high torque, andso on.

The steering column 50 is also provided with a tilt mechanism 57. Whenan operation lever 58 is operated, the steering column 50 can be tiltedaround a tilt center C with respect to a bracket 59 which is fixed tothe vehicle body side.

An intermediate shaft 64 is interposed between the output shaft 56 ofthe electric power steering apparatus 53 and a pinion shaft 61 of asteering gear unit 60 of a rack and pinion type through universal joints62 and 63 on the upper and lower sides. This intermediate shaft 64 iscomposed of a female spline (or serration) shaft 65 on the upper sideand a male spline (or serration) shaft 66 on the lower side which ispress-fitted in this female spline shaft 65.

A male serration unit 67 is formed on the male spline shaft 66 on thefront side of the vehicle, and this male serration unit 67 is fitted ina yoke 63 a of the lower-side universal joint 63 and is clamped by aclamping bolt 68.

FIG. 10 is a schematic view of the steering apparatus for a vehicleaccording to the prior art, for showing the highest level and the lowestlevel of a tilt operation (a view for explaining various axialdisplacements).

In the steering gear unit 60, a vibration is produced from the vehiclebody (on gear side) while the vehicle is running.

At assembling into the vehicle, the yoke 63 a of the lower-sideuniversal joint 63 is slid with respect to the male serration unit 67,and then the yoke 63 b of the lower-side universal joint 63 is fitted tothe pinion shaft 61, thereby clamping the clamping bolts 100 and 68.

On the intermediate shaft 64, the lower-side male spline shaft 66 ispress-fitted in the upper-side female spline shaft 65. The intermediateshaft 64 is collapsed at a collision, but is not slid in the axialdirection at a tilt operation at which the intermediate shaft 64 isnormally used. Generally, the intermediate shaft 64 is collapsed when aload of not less than 500N is applied thereon in case a collision, anaccident, or the like of the vehicle occurs and a displacement isgenerated in the axial direction.

An axial displacement due to a movement of the upper-side universaljoint caused by tilt adjustment is generated between the upper-sideuniversal joint 62 and the lower-side universal joint 63. In this case,there is provided no mechanism which slides with a low load between theupper-side universal joint 62 and the lower-side universal joint 63, sothat an axial load is generated between these joints.

Further, when torque is transmitted in a state that a position at whichthe column-assist type electric power steering apparatus 53 is installedis deviated from the designed position, a torque fluctuation becomes alittle larger with respect to the designed value.

FIG. 11 is a view for explaining that an inter-joint length changes atthe time of tilt adjustment.

The relation that LA<LB<LC is established when the inter-joint length(L) is LA at the tilt highest level position, LB at a tilt neutralposition, and LC at the tilt lowest level position.

FIG. 12 is a partially cut-away cross sectional view of the intermediateshaft according to the prior art. This intermediate shaft 64 is composedof a female spline (serration) shaft 65 on the upper side and a malespline (serration) shaft 66 on the lower side which is press-fitted inthe female spline shaft 65.

The female spline shaft 65 works also as a yoke of the upper-sideuniversal joint 62. A male serration unit 67 is formed on the malespline shaft 66 on the vehicle front side, and this male serration unit67 is fitted in a yoke 63 a of the lower-side universal joint 63 and isclamped by a clamping bolt 68.

The column-assist type electric power steering apparatus is providedwith the following function. That is, when the driver performs steeringthrough the steering wheel 52, a steering torque thereof is detected tobe calculated by CPU, and the electric motor 54 is driven on the basisof a result of the calculation. An output shaft of the electric motor 54and a steering shaft are engaged with the gear unit 55 of a worm andwheel type, and the steering power is assisted by the power of theelectric motor 54.

The intermediate shaft attached to the column-assist type electric powersteering apparatus has the following functions.

-   -   The intermediate shaft is required to have the structure which        can endure high torque transmission since it transmits high        torque constantly.    -   There should be generated no backlash in the direction of        rotation since it controls the assist of the steering torque.    -   The intermediate shaft has a collapsing mechanism for absorbing        displacement from the front part of the vehicle at a vehicle        collision in order to protect the driver.

As described above, the above functions are given to the intermediateshaft according to the prior art. However, in terms of the steeringstability, the assembling performance and the cost, these functions arenot always sufficient.

In order to satisfy the above items, such a function is required whichcan extend and contract the intermediate shaft with a low stable slidingload so that the intermediate shaft can be moved easily with a hand andcan transmit high torque without backlash.

The followings are reasons for requiring this expanding/contractingfunction.

-   -   At steering, a low stable steering shaft rotating torque        property which is not affected by a deviated position of        installation in the vehicle is to be obtained.    -   At running of the vehicle, the intermediate shaft is to absorb a        vibration and a displacement from the steering gear side so as        to make it difficult to transmit unpleasant vibration or sound        onto the steering wheel.    -   At tilt adjustment, the intermediate shaft is to easily absorb        an axial displacement when the steering wheel is tilted in an        up-and-down direction and the length of the intermediate shaft        is changed so as to prevent an extra axial load or moment from        being applied on the whole steering shaft.    -   At assembling, the intermediate shaft is to be extended and        contracted freely so as to be easily assembled in the vehicle,        whereby one clamping position in the clamping work of the        clamping bolt can be omitted.

In European Patent Application Laid-Open No. EP1078843A1, a member forpreventing backlash in the direction of rotation, which is required fora steering shaft, takes a retainer-like shape of plastic. Therefore,small gaps between the male shaft, the female shaft and the needlerollers are adjusted by such plastic members.

However, plastic products are not satisfactorily abrasion-proof and itis difficult to maintain the performance of such products withoutbacklash for a long term use. For this reason, when abrasion isproduced, there arises a problem that the backlash is generated on thesteering shaft. Since the structure is also required to allow relativemovement in the axial direction so that the male shaft and the femaleshaft are moved relatively to each other, it is required to provide agap in a sliding portion so that backlash can not be structurallyprevented completely.

In FIGS. 1 to 5 of German Patent No. DE3730393C2, in order to applypreload, there is required a structure in which leaf springs provided indifferent grooves are connected to-each other. In other cases, there isrequired a structure in which elastic members are laid under leafsprings so as to generate preload in the radial direction.

In these structures, since leaf springs having different curvatures areprovided in grooves of the male shaft and the female shaft having thecurvatures, it is very difficult to obtain a large amount of flexure ofthe leaf springs. As a result, it is very difficult to provide the leafsprings with a flexural amount which can allow fluctuations in theprocessing precision of the male shaft and the female shaft.

When torque is inputted, the male shaft, the leaf springs, balls and thefemale shaft are mutually contracted to transmit the torque, so that thepoints contacting with the balls have very high surface pressure, andthe steering shaft can highly possibly not satisfy the required torquetransmitting performance and the life as that used for a vehicle(particularly when the shaft is combined with the column-assist typeelectric power steering which is required to transmit high torque).

Since an outer leaf spring tends to slide sideways with respect to thefemale shaft at the time of torque transmission and hysteresis is easilygenerated, a structural problem that the magnitude of this hysteresiscan not be controlled.

However, in the prior art described above, even if taking JapaneseUtility Model Application Laid-Open No. 1-145670, the prior artillustrated in FIGS. 9 to 12, European Patent-Application Laid-Open No.EP1078843A1 described above, and German Patent No. DE3730393C2 describedabove into consideration, there is provided no telescopic shaft whichhas such a performance as can be combined with the column-assist typeelectric power steering apparatus. As a result, it is difficult toobtain a steering system having such an excellent performance as tosatisfy the items described above.

Under such circumstances, it is expected that a total steering system inwhich a telescopic intermediate shaft with a high performance to satisfythe above-described requirements is combined with the column-assist typeelectric power steering apparatus is to be developed.

The present invention has been contrived taking the above circumstancesinto consideration, and an object thereof is to provide a steeringapparatus for a vehicle which can transmit high torque without backlashwhen being provided with a column-assist type electric power steeringapparatus and which can extend and contract an intermediate shaft withsuch a low stable sliding load as can move the intermediate shaft easilywith a hand.

In order to achieve the above object, according to the presentinvention, there is provided a steering apparatus for a vehicle in whicha steering power of a steering shaft is assisted by a column-assist typeelectric power steering apparatus so that the steering power havingincreased torque is transmitted to steer the wheels by means of asteering mechanism in its turn, characterized in that:

a telescopic shaft with a male shaft and a female shaft fitted to eachother to be mutually unrotatable and slidable is interposed between anoutput shaft of the column-assist type electric power steering apparatusand an input shaft of the steering mechanism.

As described above, according to the present invention, since thetelescopic shaft with the male shaft and the female shaft fitted to bemutually unrotatable and slidable is interposed between the output shaftof the column-assist type electric power steering apparatus and theinput shaft of the steering mechanism, it is possible to realize astable sliding load and to prevent backlash without fail, therebytransmit torque in a state of high rigidity.

With this arrangement, the following items which are required when theintermediate shaft is combined with the column-assist type electricpower steering apparatus as described above can be fully satisfied.

-   -   At steering, a low stable steering shaft rotating torque        property which is not affected by a deviated position of        installation in the vehicle is to be obtained.    -   At running of the vehicle, the intermediate shaft is to absorb a        vibration and a displacement from the steering gear side so as        to make it difficult to transmit unpleasant vibration or sound        onto the steering wheel.    -   At tilt adjustment, the intermediate shaft is to easily absorb        an axial displacement when the steering wheel is tilted in an        up-and-down direction and the length of the intermediate shaft        is changed so as to prevent an extra axial load or moment from        being applied on the whole steering shaft.    -   At assembling, the intermediate shaft is to be extended and        contracted freely so as to be easily assembled in the vehicle,        whereby one clamping position in the clamping work of the        clamping bolt can be omitted.    -   The intermediate shaft is required to have the structure which        can endure high torque transmission since it transmits high        torque constantly.    -   Since no backlash is generated in the direction of rotation, the        assist of the steering torque can be controlled more correctly.    -   The intermediate shaft has a collapsing mechanism for absorbing        a displacement from the front part of the vehicle at a vehicle        collision in order to protect the driver.    -   The intermediate shaft is extended and contracted easily at tilt        and telescopic operations so that it is possible to obtain an        optimal position for the driver and to obtain a stable steering        property.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a steering apparatus for a vehicleaccording to a first embodiment of the present invention;

FIG. 2 is a schematic view of the steering apparatus for a vehicle shownin FIG. 1, for showing the highest level and the lowest level of tilting(a view for explaining various axial displacements);

FIG. 3 is a longitudinal cross sectional view of a telescopic shaftwhich is attached to the steering apparatus for a vehicle according tothe first embodiment of the present invention;

FIG. 4A is a cross sectional view of the telescopic shaft shown in FIG.3 in an enlarged manner, and FIG. 4B is a transverse cross sectionalview taken along the line A-A in FIG. 4A;

FIG. 5 is a transverse cross sectional view taken along the line B-B inFIG. 4A, in an enlarged manner;

FIG. 6 is a schematic view of a steering apparatus for a vehicleaccording to a second embodiment of the present invention;

FIG. 7 is a schematic view of the steering apparatus for a vehicle shownin FIG. 6, for showing a state that it is telescopically sliding;

FIG. 8 is a view for showing the center line of FIG. 7 only, in a statethat the intermediate shaft is extended and contracted by a telescopicslide;

FIG. 9 is a schematic view of a steering apparatus for a vehicleaccording to the prior art;

FIG. 10 is a schematic view of the steering apparatus for a vehicleaccording to the prior art, for showing the highest level and the lowestlevel of tilting (a view for explaining various axial displacements);

FIG. 11 is a view for explaining that an inter-joint length is changedat a tilt adjustment; and

FIG. 12 is a partially cut-away cross sectional view of the intermediateshaft according to the prior art.

EMBODIMENT OF THE INVENTION

A steering apparatus for a vehicle according to each embodiment of thepresent invention will be described below with reference to thedrawings.

First Embodiment

FIG. 1 is a schematic view of a steering apparatus for a vehicleaccording to the first embodiment of the present invention, and FIG. 2is a schematic view of the steering apparatus for a vehicle shown inFIG. 1, for showing the highest level and the lowest level of tiltingand for explaining various axial displacements.

A steering shaft 51 is rotatably supported by a steering column 50, anda steering wheel 52 is provided in an upper part of the steering shaft51.

The steering column 50 is provided with a column-assist type electricpower steering apparatus 53, and this electric power steering apparatus53 is provided with an electric motor 54 for assist, a gear unit 55serving as a reduction gear, an output shaft 56 for outputting asteering power assisted by the electric motor 54 with high torque, andso on.

The steering column 50 is also provided with a tilt mechanism 57. Whenan operation lever 58 is operated, the steering column 50 can betilt-adjusted around a tilt center C with respect to a bracket 59 whichis fixed to the vehicle body side.

A telescopic intermediate shaft 20 is interposed between an output shaft56 of the electric power steering apparatus 53 and a pinion shaft 61 ofa steering gear unit 60 of a rack and pinion type through universaljoints 21 and 22 on the upper and lower sides.

FIG. 3 is a longitudinal cross sectional view of the telescopicintermediate shaft 20 attached to the steering apparatus for a vehicleaccording to the first embodiment of the present invention. FIG. 4A isan enlarged cross sectional view of the telescopic shaft shown in FIG.3, and FIG. 4B is a transverse cross sectional view taken along the lineA-A in FIG. 4A. FIG. 5 is an enlarged cross sectional view taken alongthe line B-B in FIG. 4A.

As shown in FIG. 3 and FIGS. 4A and 4B, the telescopic shaft 20 iscomposed of a male shaft 1 and a female shaft 2 which are fitted to eachother to be mutually unrotatable and slidable.

As shown in FIG. 5, three axial grooves 3 are extended on the outerperipheral surface of the male shaft 1 at regular intervals of 120° inthe circumferential direction. To be corresponding thereto, also on theinner peripheral surface of the female shaft 2, there are provided threeaxial grooves 5 which are extended at regular intervals of 120° in thecircumferential direction.

Between the axial grooves 3 of the male shaft 1 and the axial grooves 5of the female shaft 2, a plurality of spherical members 7 (rollingmembers or balls) which are rigid bodies for rotating upon a relativemovement of the male and female shafts 1 and 2 in the axial directionare interposed to be rotatable.

Each of the axial grooves 5 of the female shaft 2 has substantially anarch-shaped or Gothic arch-shaped cross section. Each of the axialgrooves 3 of the male shaft 1 is constituted by a pair of inclinedflat-shaped side surfaces 3 a and a bottom surface 3 b which is formedto be flat between these paired flat-shaped side surfaces 3 a.

Between the axial groove 3 of the male shaft 1 and the spherical member7, a leaf spring 9 is interposed to be in contact with the sphericalmember 7 and apply preload thereto.

This leaf spring 9 has a unitary structure comprising contact portions 9a on the spherical member side to be in contact with the sphericalmember 7 at two points, contact portions 9 b on the groove surface sidewhich are separated from the contact portions 9 a on the sphericalmember side by predetermined distances substantially in thecircumferential direction and which are at the same time in contact withthe flat-shaped side surfaces 3 a of the axial groove 3 of the maleshaft 1, biasing portion 9 c each for elastically biasing the contactportion 9 a on the spherical member side and the contact portion 9 b onthe groove surface side in a direction that both the contact portions 9a and 9 b are separated from each other, and a bottom portion 9 d whichis opposed to the bottom surface 3 b of the axial groove 3.

The biasing portion 9 c is in a folded form which is folded to besubstantially U-shaped with the substantially arch-shaped bottomportion. The contact portion 9 a on the spherical member side and thecontact portion 9 b on the groove surface can be elastically biased bythe folded-shaped biasing portion 9 c to be separated from each other.

As shown in FIG. 5, three axial grooves 4 are provided to be extended onthe outer peripheral surface of the male shaft 1 at regular intervals of120° in the circumferential direction. Each of the axial grooves 4 isformed substantially at a middle position between each adjacent axialgrooves 3 in the circumferential direction. To be corresponding thereto,also on the inner peripheral surface of the female shaft 2, there areprovided to be extended three axial grooves 6 at regular intervals of120° in the circumferential direction.

Between the axial grooves 4 of the male shaft 1 and the axial grooves 6of the female shaft 2, a plurality of needle rollers 8 which arecolumnar members of rigid bodies for slidably moving upon a relativemovement of the male shaft 1 and the female shaft 2 in the axialdirection are interposed with very small gaps. Each of these axialgrooves 4 and 6 has substantially an arch-shaped or Gothic arch-shapedcross section.

As shown in FIG. 4A, at an end portion of the male shaft 1, the needleroller 8, the leaf spring 9 and the ball 7 are fixed in the axialdirection by a stopper plate 11, a washer holder 12, a wave washer 13and a push nut 14.

The stopper plate 11 comprises a surface against which the needle roller8 or the ball 7 is directly abutted. The wave washer 13 serves toappropriately preload the needle roller 8 through the stopper plate 11in the axial direction, whereby the needle roller 8 can freely move inthe axial direction to prevent abnormal sound from being generated.

The push nut 14 serves to perform fixation in the axial direction. Thepush nut 14 in itself can be fixed in the axial direction satisfactorilyby being fitted into the shaft to be applied. However, in case of thepresent embodiment, in order to obtain higher fixing capability in theaxial direction, it is designed such that an annular groove 15 is formedon the shaft so that the push nut 14 is to be fitted in the annulargroove 15.

The push nut 14 and the wave washer 13 are formed as separate members,but are connected to each other by the washer holder 12 as a unitarystructure. A pawl 16 is protruded from the washer holder 12. The pawl 16catches the push nut 14 to hold in such a manner as to sandwich the wavewasher 13 therebetween. This arrangement is made to reduce the number ofthe constituent parts, for the purpose of reducing the number of stepsin assembling. In this respect, the pawl may be formed to be protrudedfrom the stopper plate 11 in the same manner, so that the waver washer13 and the push nut 14 can be formed as a unitary structure. It ispossible to arrange such that the washer holder 12 described above isremoved, a coned disk and a flat washer are used instead of the wavewasher 13 and the push nut 14, respectively, and the outer peripheralpart of the flat washer is fixed by plastically deforming by caulking(orclinching), instead of the pawl 16. In this case, the number of theconstituent parts can be reduced, and the cost of the constituent partscan be decreased.

Further, a lubricating agent is applied among the axial grooves 3 and 4of the male shaft 1, the axial grooves 5 and 6 of the female shaft 2,the leaf springs 9 and the spherical members 7, so that the male shaftand the female shaft can slide in the axial direction with a stablesliding load without backlash at the time of non-transmission of torque(at the time of sliding movement).

In other words, the telescopic shaft 20 is provided with a first torquetransmitting device comprising first interposing portions (the axialgrooves 3 and 5) which are formed on the outer peripheral surface of themale shaft 1 and on the inner peripheral surface of the female shaft 2,first torque transmitting members (the rolling members 7) which areformed on the first interposing portions (the axial grooves 3 and 5) andare rotated upon a relative movement in the axial direction of the maleshaft 1 and the female shaft 2, and elastic members (the leaf springs 9)which are disposed in the first interposing portions (the axial grooves3 and 5) in adjacent to the first torque transmitting members (therolling members 7) in the radial direction so as to restrain the firsttorque transmitting members (the rolling members 7) at rotation and toapply preload to the male shaft 1 and the female shaft 2 through thefirst torque transmitting members (the rolling members 7) atnon-rotation, and a second torque transmitting device comprising secondinterposing portions (the axial grooves 4 and 6) which are formed on theouter peripheral surface of the male shaft 1 and on the inner peripheralsurface of the female shaft 2 and second torque transmitting members(the sliding members 8) which are formed on the second interposingportions (the axial grooves 4 and 6) and are slid upon a relativemovement in the axial direction of the male shaft 1 and the female shaft2 and to transmit torque at rotation thereof.

In the telescopic shaft having such a structure as described above,since the spherical members 7 are interposed between the male shaft 1and the female shaft 2 and the spherical members 7 are preloaded by theleaf springs 9 to the extent that no backlash is generated with respectto the female shaft 2, it is possible to securely prevent backlashbetween the male shaft 1 and the female shaft 2 at the time ofnon-transmission of torque. At the same time, the male shaft 1 and thefemale shaft 2 can slide with a stable sliding load with no backlashwhen they are moved in the axial direction relatively to each other.

At the time of transmission of torque, the leaf springs 9 areelastically deformed to restrain the spherical members 7 in thecircumferential direction, and the three columnar members 8 interposedbetween the male shaft 1 and the female shaft 2 mainly perform thefunction of transmitting torque.

For example, when torque is inputted from the male shaft 1, sincepreload of the leaf spring 9 is applied in the initial stage, there isgenerated no backlash and the reaction force against the torque isgenerated by the leaf spring 9, thereby transmitting the torque. In thiscase, the torque transmission as a whole is performed in a state thatthe transmitted torque and the inputted torque between the male shaft 1,the leaf springs 9, the spherical members 7 and the female shaft 2 arein balance.

When the torque is further increased, a gap between the male shaft 1 andthe female shaft 2 through the columnar members 8 in the direction ofrotation disappears so that the columnar members 8 transmits anincremental portion of the torque subsequent thereto through the maleshaft 1 and the female shaft 2. For this reason, it is possible tosecurely prevent backlash in the direction of rotation between the maleshaft 1 and the female shaft 2 so as to transmit the torque in a stateof high rigidity.

From the above description, according to the present embodiment, sincethe columnar members 8 are provided in addition to the spherical members7, almost all of the load amount can be supported by the columnarmembers 8 when a great amount of torque is inputted. As a result, it ispossible to suppress an increase of the contact pressure between theaxial grooves 5 of the female shaft 2 and the spherical members 7 so asto improve the durability of the shaft. At the same time, when a torqueload is great, it is possible to transmit the torque in a state of highrigidity.

Moreover, since the columnar members 8 are in contact with the maleshaft 1 and the female shaft 2, it is possible to reduce the torsionaltorque toward the spherical members 7 and to suppress sideway slide ofthe leaf springs 9. As a result, it is possible to prevent thehysteresis from being excessively great.

As described above, according to the present embodiment, it is possibleto realize a stable sliding load and, at the same time, to securelyprevent backlash in the direction of rotation, thereby transmitting thetorque in a state of high rigidity.

Note that the spherical members 7 are preferably balls of rigid bodies.It is also preferable that the columnar members 8 of rigid bodies areneedle rollers.

Since the columnar member (hereinafter called the needle roller) 8receives a load thereof with a line contact, there can be obtainedvarious advantages including that the contact pressure can be lowered,compared with the case with a ball which receives a load with a pointcontact. As a result, this arrangement is superior in the followingpoints to a case in which all of the rows are in ball rolling structure.

-   -   The attenuating performance in the sliding portion is great,        compared with that in the ball rolling structure. As a result,        the vibration absorbing performance is high.    -   Since the needle roller is slightly in contact with the male        shaft and the female shaft, a fluctuation in sliding load can be        kept low, and a vibration due to this fluctuation is not        transmitted to the steering.    -   If the same amount of torque is to be transmitted, the contact        pressure can be kept lower in the needle roller structure. As a        result, the length in the axial direction can be reduced so that        the space can be used effectively.    -   If the same amount of torque is to be transmitted, the contact        pressure can be kept lower in the needle roller structure. As a        result, an additional process for hardening the surfaces of the        axial grooves of the female shaft by thermal treatment or the        like is no longer required.    -   The number of the constituent parts can be reduced.    -   The assembling performance can be improved.    -   The assembling cost can be reduced.

As described above, the needle rollers play the essential role fortorque transmission between the male shaft 1 and the female shaft 2 and,at the same time, are brought into sliding contact with the innerperipheral surface of the female shaft 2. This structure is superior inthe use of the needle rollers in an intermediate shaft joint to theconventional structure which employs spline fitting in the followingrespects.

-   -   The needle rollers are manufactured in mass production, and can        be manufactured at very low cost.    -   The needle rollers are polished after being subjected to the        thermal treatment, so that they have high surface hardness and        excellent abrasion fastness.    -   Since the needle rollers have been polished, they have fine        surface roughness and a low coefficient of friction in a sliding        movement. As a result, the sliding load can be kept low.    -   Since the length or the layout of the needle rollers can be        changed in accordance with the condition of use, the needle        rollers can be used in various applications without a change of        the design concept.    -   There is a case in which the coefficient of friction in a        sliding movement is required to be further lowered, depending on        the condition of use. In such a case, the sliding        characteristics can be changed by subjecting only the needle        rollers to the surface treatment. As a result, the needle        rollers can cope with various applications without a change of        the design concept.    -   Since the needle rollers having different outer diameters by        several microns can be manufactured at low cost, the gap among        the male shaft, the needle rollers, and the female shaft can be        minimized by selecting a diameter of the needle rollers. As a        result, the rigidity of the shaft in the torsional direction can        be improved easily.

Next, as shown in FIG. 2, all of such problems as described below can besolved.

-   -   A vibration is generated from the vehicle body (on the gear unit        side) at running in the steering gear unit 60. However, in the        present embodiment, since the telescopic shaft 20 can be easily        extended and contracted owing to a low sliding load, the        vibration from the vehicle body (on the gear side) can be fully        absorbed.    -   At assembling into the vehicle, conventionally as shown in FIG.        10, the yoke 63 a of the lower-side universal joint 63 is slid        with respect to the male serration unit 67 so that the yoke 63 b        of the lower-side universal joint 63 is brought into fitting        with the pinion shaft 61, to be finally clamped by the clamping        bolt 68. However, in case of the present embodiment, a yoke of        the universal joint 22 and the male shaft 1 are formed as a        unitary structure so that the telescopic shaft 20 can be        extended and contracted more easily with a low sliding load. As        a result, the assembling work can be performed easily, the        assembling performance can be improved, and the manufacturing        cost can be reduced. Also, with this arrangement, it is no        longer required to perform a clamping work of the clamping bolt        68.    -   Also, according to the prior art as shown in FIG. 10, an axial        load is generated due to a movement of the upper-side universal        joint caused by tilt adjustment between the upper-side universal        joint 62 and the lower-side universal joint 63. However, in the        present embodiment, since the telescopic shaft 20 can be        extended and contract more easily with a low sliding load, such        an axial load is not generated.    -   Further, according to the prior art shown in FIG. 10, when        torque transmission is performed in a state that a position of        installation of the column-assist type electric power steering        apparatus 53 is deviated from the designed value, the torque is        slightly fluctuated with respect to the designed value. However,        in the present embodiment, since the telescopic shaft 20 can be        extended and contract more easily with a low sliding load, the        torque is not fluctuated greatly with respect to the designed        value.

From the above description, it is possible to fully satisfy thefollowing requisitions which are required for a case in which theintermediate shaft is combined with the column-assist type electricpower steering apparatus.

-   -   At steering, a low stable steering shaft rotating torque        property which is not affected by a deviated position of        installation in the vehicle is to be obtained.    -   At running of the vehicle, the intermediate shaft 20 is to        absorb a vibration and a displacement from the steering gear        unit 60 so as to make it difficult to transmit unpleasant        vibration or sound onto the steering wheel 52.    -   At tilt adjustment, the intermediate shaft 20 is to easily        absorb an axial displacement when the steering wheel 52 is        tilted in an up-and-down direction and the length of the        intermediate shaft 20 is changed so as to prevent an extra axial        load or moment from being applied on the whole steering shaft        52.    -   At assembling, the intermediate shaft is to be extended and        contracted freely so as to be easily assembled in the vehicle,        whereby one clamping position in the clamping work of the        clamping bolt 68 can be omitted.    -   The intermediate shaft is required to have the structure which        can endure high torque transmission for transmitting high torque        constantly.    -   No backlash is to be generated in the direction of rotation so        that the assist control on the steering torque can be performed        more correctly.    -   The intermediate shaft is required to have a collapsing        mechanism for absorbing a displacement from the front part of        the vehicle at a collision in order to protect the driver.    -   The intermediate shaft is to be extended and contracted easily        at a tilt operation so that it is possible to obtain an optimal        position for the driver and to obtain a stable steering        property.

Second Embodiment

FIG. 6 is a schematic view of a steering apparatus for a vehicleaccording to the second embodiment of the present invention. FIG. 7 is aschematic view of the steering apparatus for a vehicle shown in FIG. 6,for showing a state that it is telescopically sliding. FIG. 8 is a viewonly for showing the center line of FIG. 7, in a state that anintermediate shaft is extended and contracted by the telescopic sliding.

The second embodiment has a column structure which is provided with atelescopic function, in addition to a tilt function, so that the wholesteering column 50 can move in the axial direction. In such a case, theintermediate shaft 20 is required to be extended and contracted freely.

As shown in FIG. 6, an elongated hole 31 for telescopic operation isformed on a bracket 59 which is fixed to the vehicle body side, andanother elongated hole 33 for telescopic operation is formed on adistance bracket 32 which is provided on the steering column 50.

As shown in FIG. 7, the position of the upper-side universal joint 21 ischanged owing to telescopic adjustment. In this case, however, theintermediate shaft 20 can absorb an axial displacement easily so that anextra axial load or moment is not applied on the whole steering shaft.

As shown in FIG. 8, the relation that Lf<Le<Ld is established when theinter-joint length (L) is Ld at the maximum telescopic position, Le at atelescopic intermediate position, and Lf at the minimum telescopicposition.

As seen from the above description, also in the second embodiment, it ispossible to fully satisfy the following requisitions which are requiredfor a case in which the intermediate shaft is combined with thecolumn-assist type electric power steering apparatus.

-   -   At steering, a low stable steering shaft rotating torque        property which is not affected by a deviated position of        installation in the vehicle is to be obtained.    -   At running of the vehicle, the intermediate shaft 20 is to        absorb a vibration and a displacement from the steering gear        unit 60 so as to make it difficult to transmit unpleasant        vibration or sound onto the steering wheel 52.    -   At telescopic adjustment, the intermediate shaft 20 is to easily        absorb an axial displacement when the steering wheel 52 is        telescopically slid and the length of the intermediate shaft 20        is changed so as to prevent an extra axial load or moment from        being applied on the whole steering shaft 52.    -   At assembling, the intermediate shaft is to be extended and        contracted freely so as to be easily assembled in the vehicle,        whereby one clamping position in the clamping work of the        clamping bolt 68 can be omitted.    -   The intermediate shaft is required to have the structure which        can endure high torque transmission for transmitting high torque        constantly.    -   No backlash is to be generated in the direction of rotation so        that the assist control on the steering torque can be performed        more correctly.    -   The intermediate shaft is required to have a collapsing        mechanism for absorbing a displacement from the front part of        the vehicle at a collision in order to protect the driver.    -   The intermediate shaft is to be extended and contracted easily        at a telescopic operation so that it is possible to obtain an        optimal position for the driver and to obtain a stable steering        property.

Note that the present invention is not limited to the embodimentsdescribed above, but can be altered in various manners.

As described above, according to the present invention, it is possibleto realize a stable sliding load and, at the same time, to preventbacklash without fail to transmit torque in a state of high rigidity.

1. A steering apparatus for a vehicle, in which steering power of asteering shaft is assisted by a column-assist type electric powersteering apparatus so that the steering power is transmitted to steerwheels of the vehicle by a steering mechanism, comprising: a telescopicshaft with a male shaft and a female shaft fitted to each other to becapable of transmitting torque therebetween and moving in an axialdirection relative to each other, said telescopic shaft being interposedbetween an output shaft of said column-assist type electric powersteering apparatus and an input shaft of the steering mechanism, saidtelescopic shaft being provided with: a first torque transmitting deviceincluding first interposing portions which are formed on an outerperipheral surface of the male shaft and an inner peripheral surface ofthe female shaft, first torque transmitting members which are disposedin the first interposing portions and are rotated upon relative movementof the male shaft and the female shaft in the axial direction, andelastic members which are disposed in the first interposing portionsadjacent to the first torque transmitting members so as to restrain thefirst torque transmitting members during torque transmission between themale and female shafts and to apply preload to the male shaft and thefemale shaft through the first torque transmitting members when notorque is transmitted between the male and female shafts; and a secondtorque transmitting device including second interposing portions whichare formed on the outer peripheral surface of the male shaft and on theinner peripheral surface of the female shaft, and second torquetransmitting members constituted by discrete columnar bodies which aredisposed in the second interposing portions, which slide upon relativemovement of the male shaft and the female shaft in the axial direction,and which transmit torque during torque transmission between the maleand female shafts.
 2. The steering apparatus according to claim 1,wherein the first interposing portions include at least one pair ofaxially extending grooves formed on an outer peripheral surface of themale shaft and an inner peripheral surface of the female shaft, and thefirst torque transmitting members include a plurality of sphericalmembers disposed in the at least one pair of axially extending grooves.3. The steering apparatus according to claim 1, wherein the secondinterposing portions include at least one pair of axially extendinggrooves formed on an outer peripheral surface of the male shaft and aninner peripheral surface of the female shaft, and at least one of thecolumnar bodies is disposed in the at least one pair of axiallyextending grooves.
 4. The steering apparatus according to claim 1,wherein the second torque transmitting members are arranged so as not totransmit torque until at least one of the elastic members hassufficiently deformed such that the second torque transmitting memberscome into direct torque-transmitting contact with both the male andfemale shafts.
 5. The steering apparatus according to claim 1, whereineach first interposing portion includes a pair of first axiallyextending grooves formed on an outer peripheral surface of the maleshaft and an inner peripheral surface of the female shaft, and eachsecond interposing portion includes a pair of second axially extendinggrooves formed on an outer peripheral surface of the male shaft and aninner peripheral surface of the female shaft.
 6. The steering apparatusaccording to claim 5, wherein the pair of first axially extendinggrooves includes a groove constituted by a pair of inclined flat-shapeside surfaces and a flat bottom surface formed between the sidesurfaces, and a groove constituted by an arch-shaped or Gothicarch-shaped surface.
 7. The steering apparatus according to claim 5,wherein each groove of the pair of second axially extending grooves isconstituted by an arch-shaped or Gothic arch-shaped surface.
 8. Asteering apparatus for a vehicle, in which steering power of a steeringshaft is assisted by a column-assist type electric power steeringapparatus so that the steering power is transmitted to steer wheels ofthe vehicle by a steering mechanism, comprising: a telescopic shaft witha male shaft and a female shaft fitted to each other to be capable oftransmitting torque therebetween and moving in an axial directionrelative to each other, said telescopic shaft being interposed betweenan output shaft of said column-assist type electric power steeringapparatus and an input shaft of the steering mechanism, said telescopicshaft being provided with: a first torque transmitting portion includinga first pair of axially extending grooves which are respectively formedon an outer peripheral surface of the male shaft and an inner peripheralsurface of the female shaft, a first torque transmitting member which isreceived in the first pair of axially extending grooves and is rotatedupon relative movement of the male shaft and the female shaft in theaxial direction, and an elastic member which is disposed in one of thefirst pair of axially extending grooves so as to elastically support thefirst torque transmitting member; and a second torque transmittingportion including a second pair of axially extending grooves which arerespectively formed on the outer peripheral surface of the male shaftand on the inner peripheral surface of the female shaft, and a discretecolumnar body which is received in the second pair of axially extendinggrooves and which slides upon relative movement of the male shaft andthe female shaft in the axial direction, wherein the second torquetransmitting portion is constructed so as not to transmit torque in afirst range of torque transmitted between the male and female shafts andto become effective to transmit torque in a second range of torquetransmitted between the male and female shafts, the second range oftorque being higher than the first range of torque.
 9. The steeringapparatus according to claim 8, wherein the elastic member is disposedso as to restrain the first torque transmitting member during torquetransmission between the male and female shafts and to apply preload tothe male and female shafts through the first torque transmitting memberwhen no torque is transmitted between the male and female shafts. 10.The steering apparatus according to claim 8, wherein the first torquetransmitting member is a spherical member.
 11. The steering apparatusaccording to claim 8, wherein the first pair of axially extendinggrooves includes a groove constituted by a pair of inclined flat-shapeside surfaces and a flat bottom surface formed between the sidesurfaces, and a groove of constituted by an arch-shaped or Gothicarch-shaped surface.
 12. The steering apparatus according to claim 8,wherein each groove of the second pair of axially extending grooves isconstituted by an arch-shaped or Gothic arch-shaped surface.